APPROVED BIOLOGICAL CONTROL AGENTS
The Aphthona species complex consists of six different species all with a similar biology. The larval stage is the most destructive whereby the larvae feed on fine and lateral spurge roots, impairing the roots and preventing moisture and nutrient uptake. Additionally, the root-feeding provides entry points for deleterious pathogens.
Aphthona spp. overwinter in the spurge roots as larvae which can be found from July to early spring of the following year. Pupation occurs in the soil near the plant with adult emergence occurring in June, July, and August.
Adult feeding damages the host and reduces the plant’s ability to make sugars for root reserves. The effective species in the genus Aphthona spp. are typically best suited for dry sites with a large amount of sun exposure. Recent studies suggest that these insects can also be used as a “bio-herbicide” in riparian areas as well. Apthona are hardy insects that can be stored for several days if packaged correctly. Initial releases into areas containing high ant or grasshopper populations should be avoided.
Adult Oberea erythrocephala, or the red-headed leafy spurge stem borers, are characterized by their red heads, black eyes, and slender bodies with antennae that are nearly as long as the body.
The males emerge several days before the females and both sexes are sexually immature for two weeks. Adults deposit eggs from the end of June to mid-July. Females often girdle the upper part of the stem, gnaw a hole into the stem above the girdle, and deposit an egg into the hole. Each female can produce approximately 60 eggs during her lifetime. The larvae hatch 10 days after oviposition and feed on the pith, tunneling downward toward the crown where they remain during the winter. The mined stems dry, wilt and do not produce flowers or seeds.
The destructive feeding in the crown and root reduces the plant’s root reserves and allows pathogenic fungi to enter the leafy spurge roots. This agent prefers mesic areas with trees and can survive subfreezing winter temperatures. They are easiest to collect during the morning hours with a sweep net or by hand. Some research suggests that this agent may be biotype specific – only attacking certain biotypes of leafy spurge.
Approved Biological Control Agents for release in Idaho: